Dialysis membranes and devices perform important life sustaining functions when used in artificial kidneys and other types of filtration devices. A well recognized problem of high flux dialyzers is the back filtration from dialysate to the blood of undesirable molecules. Due to the high cost of using sterile, pyrogen-free dialysates, it would be highly desirable to have available a dialysis membrane which could remove relatively large solutes such as .beta.-2 microglobulin while preventing passage of similarly sized molecules from dialysate to blood. Membranes, however, which offer a high rate of diffusion of solutes from the blood to dialysate also suffer from high rates of back diffusion of solutes from dialysate back to the blood. Similarly, existing membranes which offer a high rate of convection also suffer from high rates of back filtration. A need has therefore existed for dialysis membranes which provide for adequate removal of uremic toxins from the blood while preventing back transport of undesirable substances to the blood. Similarly, other fluid filtration processes benefit from the availability of membranes having such rectifying properties.
A need has also existed for devices such as bioreactors in which rectifying membranes provide a means for simultaneously supplying nutrients to and carrying products and waste byproducts from live cells that are used to make products which cannot be economically produced by traditional synthetic chemistry techniques.